Okay, so I think you guys have me convinced to tackle the XR-VCO as the next Magic Smoke PCB. In my reading, I found the version in the VCO Chip Cookbook uses the LM3046 NPN transistor array, while the version in AS21C uses the LM394 matched pair. I think I'm going to go with the LM394 version because that part is still available at Futurlec for a very good price, and you can also sub the MAT-02 or the SSM2210 pairs (same pinout as the 394) for better performance, although with a higher price. You can even go with a pair of hand-matched 2N3904s if you want the least expensive option. The LM3046 / 3086 show good performance, but this part is getting increasingly tougher to find.

I'm also looking at adding a PWM out based on the Sine/Tri-Saw output. Should give some interesting results as the Tri-Saw wave is skewed (will go one octave up as the Tri wave is skewed from triangle to the octave up Saw). One more possible addition - a suboctave from the PWM out, and a separate suboctave from the Square out. I still have to test these new waveforms, but I think they'll be interesting additions. Stay tuned to this channel...

I'll be prototyping this weekend. I'll let everyone know how it sounds and what additions (if any) I'll be making to the XR VCO. I've got the schematic entered, but I want to breadboard all of this to make sure it all works as I think it should.

Recorded a quick sample last night. I think this is going to be a very cool VCO!

Start: Triangle being modulated via the Skew control with a slow LFO. It's a subtle effect, but very nice as the wave goes from Tri to 2X Saw.

21 Seconds: This is the Pulse output, with the pulse width being modulated by an LFO. Very thick PWM sound.

36 Seconds: Still listening to the Pulse output only, but now we have the Triangle wave being modulated by one LFO, while the pulse width is being modulated by a second LFO. The effect is very dramatic and a little unpredictable (in a good way). As the Triangle (which is the input to the Pulse comparator) changes shapes and morphs to the 2X saw, the Pulse wave also changes and goes to 2X frequency with the saw. Using two separate LFOs gives some very complex animation. I actually removed the hysterisis from the pulse comparator to slow it down so that the appearance of the 2X pulse wouldn't "pop" so much. I like the way it comes in now.

55 seconds: Now we hear the Tri/Saw wave along with the Pulse wave. Again, one LFO is modulating the Triangle Skew, and another slightly faster LFO is modulating the pulse width. This part has a little reverb/delay added and it sounds pretty massive for just ONE oscillator. And I didn't even add the sub-octaves.

The MP3 encoding has a bit of high frequency 'hash' that wasn't there on the original, but I think I tamed it with a little bit of high cut. Whaddaya guys and gals think? I'm done with the prototyping, so I'm on to the PCB layout stage.

I ran into a couple XR2206s at Halted Electronics in Santa Clara a month or so ago in their surplus bin. So I have a few burning a hole in my drawer of miscellaneous undedicated parts. Would love to get my hands on an XR-VCO board when you get them genned up. Plz count me in.
Thx
Joe

Good find on the Mouser part number. I looked at Mouser and Digi-Key and couldn't find it at either place.

Luckily, this part is still in production. If you played your cards right, you MIGHT be able to wangle some samples from Exar. Companies are being a little tighter with samples these days though, so that might not be the easiest route. However, Futurlec shows the 2206 in stock for about 5 dollars, and Jameco has them for about $5.50 (I got mine there because they're on my way home from work). When the boards are ready, I can swing by Jameco and grab some. Let me know when you order a board, and for $7.00 I'll add the 2206 chip (includes shipping and the sales tax I have to pay at Jameco). The other 'tough' parts include the 2k tempco (Magic Smoke carries these), and the NPN matched pair. You can use two 2N3904s, the LM394 pair (Futurlec), or the SSM2010, depending on the level of performance you need and your budget.

Good find on the Mouser part number. I looked at Mouser and Digi-Key and couldn't find it at either place.

Luckily, this part is still in production. If you played your cards right, you MIGHT be able to wangle some samples from Exar. Companies are being a little tighter with samples these days though, so that might not be the easiest route. However, Futurlec shows the 2206 in stock for about 5 dollars, and Jameco has them for about $5.50 (I got mine there because they're on my way home from work). When the boards are ready, I can swing by Jameco and grab some. Let me know when you order a board, and for $7.00 I'll add the 2206 chip (includes shipping and the sales tax I have to pay at Jameco). The other 'tough' parts include the 2k tempco (Magic Smoke carries these), and the NPN matched pair. You can use two 2N3904s, the LM394 pair (Futurlec), or the SSM2010, depending on the level of performance you need and your budget.

Tim (waves "Hi" to Jameco on my way home) Servo

Fantastic Tim!

I'll let the Mouser order slide on these and get them with the PCB's! Brilliant ~ thank you sire

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